If you didn't get the filter attached properly it could be sucking air causing
the shift problem, but I would try resetting the ECM first to see if that
helps. If not then I would drop the pan and double check the filter.

Depending on the transmission.Many gm trans. have an A and B switch
in the trans. When you removed the trans. pan , is it possible you
knicked the switch (a miniature motor really) in the trans?. A controls
gear 1 and 2. B gears 3 and 4.The tabs on these motors are very delicate
and break off them easily.

Yes I had the shift problem before I
changed the filter that's why we
changed the filter, & it's running
smoother and seems better but it
won't shift gears after 25-30mph &
what's the ecm & how do I do that?

The switch is easy to check, once inside of pan again. Look at the 2
wires on the switches ( they're actually little electronic motors). If any tab
is broken replace it. It is held on by a small fastener behind the actuator.
Check the link I shared and it should show the switch upclose as well as
hardware. It sounds like the B switch.Classic symptom you describe.

I think it's either the 3-4 accumulator spring in the valve body maybe broken or the 3-4 clutch discs in the transmission are worn out. Anyway I just found a Tech Manual for your trans. http://www.grail-ss.com/GRAIL%20Website%20Files/4L60ETechGuide.pdf

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